Do we even need a WebML API? There's already WASM and WebGPU. What can't you do with those?
The point made above is that WebGPU can only be used for GPU's and not really for other types of 'neural accelerators' (like e.g. the ANE on Apple devices).
Accelerators inside GPU (like Tensorcores) seems like a lot better deal as you can easy utilize it without 4 abstraction layers with only some unknown to us mortals operations support inside. (And my god i hope apple will allow to programmable run ANE or at least put this api inside Metal framework cause right now working with Coreml for anything new is a nightmare and even some old models are broken on new versions of coremltools)